Dr. Ulrich Brinkmann has recently identified a gene termed CAS which encodes a phosphoprotein that is localized to microtubules and to the mitotic spindle. CAS is the mammalian homologue of CSE1, a yeast gene which controls mitosis. Several lines of evidence suggest CAS has a similar role in mammalian cells: One is that CAS levels correlate with cell growth. Another is that CAS antisense RNA blocks mitosis and Gl-S transition in Hela cells. Because CAS expression is high in proliferating cells, anti-CAS antibodies can be used as a proliferation marker in leukemia/lymphoma cells. CAS is located at 20q13, a region that is amplified in some breast, colon and uroepithelial cells. We are investigating the role of CAS in these types of tumors.